Surface smoothing of rough amorphous films by irradiation-induced viscous flow

Surface roughening and smoothing reactions on vapor codeposited glassy Zr₆₅Al_7.5Cu_27.5 films by 1.8 MeV Kr⁺ ion beam irradiation is investigated. Irradiation causes significant smoothing of initially rough surfaces, and nearly atomically smooth films can be achieved. Smooth surfaces roughen at high doses and long wavelengths. By a Fourier analysis, radiation-induced viscous flow is identified as the dominant surface relaxation mechanism. Two noise terms are identified, which operate on different length scales: One is due to sputtering and the other to thermal spikes. The irradiation-induced viscosity is compared with radiation-enhanced diffusion.